Process of separating air into an oxygen-rich fraction suitable for blast furnace operation

ABSTRACT

In a process for separating air into an oxygen rich fraction. The gas to be separated is compressed to a high pressure and cooled to almost the liquefaction temperature. A portion of the cooled gas is liquefied and passed through a rectification column. Another portion of the resultant cooled gas is heated and engine expanded and then passed to the rectification column to be placed in heat transfer relationship with the liquid portion.

United States Patent Becker Oct. 24, 1972 [541 PROCESS OF SEPARATING AIR INTO AN OXYGEN-RICH FRACTION SUITABLE FOR BLAST FURNACE OPERATION [72] Inventor: Rudolf Becker, Munich-Solln, Germany [73] Assignee: Linde Aktiengesellschaft,

Wiesbaden, Germany [22] Filed: July 22, 1969 [21] Appl.No.: 849,556

, Related us. Application Data [63] Continuation of Ser. No. 590,391, Oct. 28,

1966, abandoned.

[30] Foreign Application Priority Data Oct. 29, 1965 Germany ..L 52016 [52] US. Cl ..62/13, 62/38 [51] Int. CI..... ..F25j'3/00 [58] Field of Search ..62/38-39, 13-15 [56] References Cited UNITED STATES PATENTS 2,460,859 2/1949 Trumpler ..62/14 2,737,784 3/1956 Becker ..62/14 X 2,924,078 2/ 1960 Tsunoda ..62/14 UX 2,964,914 12/1960 Schuftan et al.. ..62/14 2,984,079 5/1961 Matsch et a1 ..62/18 UX 3,110,155 11/1963 Schaftan ..62/38 X Primary Examiner-Norman Yudkoff Attorneyl. William Millen 7] ABSTRACT In a process for separating air into an oxygen rich fractiomThe gas to be separated is compressed to a high pressure and cooled to almost the liquefaction temperature. A portion of the cooled gas is liquefied and passed through a rectification column. Another portion of the resultant cooled gas is heated and engine expanded and then passed to the rectification column to be placed in heat transfer relationship with the liquid portion.

6 Claims, 2 Drawing Figures PATENTEU E 2 4 I97? 3 6 99 .695

In TOR RUDOLF KER A ORNEY PROCESS OF SEPARATING AIR INTO AN OXYGEN-RICH FRACTION SUITABLE FOR BLAS I FURNACE OPERATION This application is a continuation of co-pending application, Ser. No. 590,391 filed Oct. 28, 1966 and now abandoned.

This invention relates in general to the low temperature separation of gases. In particular, this invention re-' lates to improvements in a process for the separation of air into a fraction enriched in nitrogen and a fraction enriched in oxygen by compressing air to be'separated; cooling resultant compressed air to almost the condensation temperature; branching a portion of resultant cooled compressed air; liquefying resultant branched portion; passing resultant liquid to the top part of a rectifying column; and passing another portion of said resultant cooled compressed air to the bottom part of said rectification column. I

In German Pat. No. 589,916 of Dec. 20, 1933, a mode of operation is described wherein a portion of the air is passed in heat exchange with the oxygen-rich mixture, is completely liquefied, and is then introduced into the rectification apparatus. The refrigeration ener- 'gy necessary for conducting such a process can be obtained by engine expanding the gaseous nitrogen-rich mixture withdrawn from the rectification column. This old process is satisfactory for some purposes, but it is not the most economical from an overall standpoint. This problem of economics is especially acute when it is desired to produce oxygen-enriched blast air for the blast furnace industry, with the least possible expenditure with respect to initial investment and operating costs.

An object of this invention therefore is to provide an improved process for the production of oxygen in a concentration suitable for blast furnace operation.

' Another object is to provide a process for the production of oxygen which entails a comparatively low expenditure with respect to initial investment and operating costs.

Another object is to provide an improved low temperature process for the production of fractions enriched in at least one component.

Upon further study of the specification and claims, other objects and advantages of the present invention will become apparent.

For the attainment of the above objects there is provided in a process comprising a. compressing gas-to-be-separated to a higher pressure;

b. cooling resultant higher pressure gas to almost the liquefaction temperature;

0. branching a portion of resultant cooled higher pressure gas; 7

d. liquefying resultant branched portion;

e. passing resultant liquid to fractionating apparatus; and

f. passing another portion of resultant cooled higher pressure air to said fractionating apparatus whereby said resultant liquid and said another portion are placed in heat transfer relationship; the improvement comprising the intermediate step of heating said another portion of resultant cooled higher pressure gas, and engine expanding resultant heated another portion prior to passing said another portion to said fractionating apparatus.

Though this invention is applicable to the separation of any gaseous mixture, it is particularly useful for theproduction of blast furnace grade oxygen from air. Consequently, the following description, though pertaining to air fractionation, is not to be considered a limitation of the broad aspects of this invention.

in this connection, the air-to-be-separated is preferably compressed to a pressure of about l-2 atmospheres gauge. After engine expansion, preferably through a turbine, the pressure thereof drops to tion temperature by heat exchange with separation products, preferably in a regenerator, and can then be reheated in anotherheat exchanger. It is preferred, however, that only a part, preferably to 97 percent of said portion of the-air to be engine expanded be so cooled. The other part can then be withdrawn from the deep cooling heat exchanger at a position where it has a temperature of about 130230, preferably 200 to 220 K. This withdrawn stream should in any event have a temperature at least about 40 C., preferably about C. higher than the deeply cooled air. The

higher temperature withdrawn air is then freed fromcarbon dioxide by a technique such as adsorption which does not require any further temperature reduction. The resultant higher temperature CO -free stream is then admixed to the other part of the deeply cooled air which is to be engine expanded.

As to the fractionating apparatus, it is preferred to employ a rectifying column, although it is also possible.

to employ alternative devices such as a partial evaporator or partial condenser, for example, that illustrated in German Pat. No. 589,916.

in a preferred embodiment, not all of the air is compressed to that pressure necessary to engine expansion. In this way about preferably 30 to 34 percent of the total air is compressed to an intermediate pressure of preferably about 1.] to 1.3 atmospheres absolute, and after cooling thereof, is passed into the rectifying column.

Advantageously, at least one of the two separation products is withdrawn by applying a vacuum to the deep cooling heat exchangers.

The energy produced in the expansion turbine is preferably utilized for air compression, or for the intake and compression of the oxygen product suitably by a direct coupling of the turbine and the compressor.

The rectification in the fractionating column thus takes place at only a slight superatmospheric pressure, or also at subatmospheric pressure, the preferred range being 0.8 to 1.2 atmospheres absolute. Owing to the fact that the curvature of the rectification equilibrium curve increases with decreasing pressures, it is possible, by rectification at low pressures, to attain a higher oxygen yield, using the same amount of reflux as in the case of higher pressures. This is a distinct advantage over the previously known processes which operate under a higher pressure.

Referring now to the drawing,

FIGS. 1 and 2 are schematic illustrations of two preferred embodiments of this invention.

Referring specifically to FIG. 1, the air introduced through conduit 1 is compressed in compressor 2 to 2.3

atmospheres absolute, and is passed, throughconduit 3, to the reversible interchangeable regenerators 4 or 5 (illustrated: 4) wherein air is cooled by the nitrogen-enriched separation product, and to the regenerators 6 or 7 (illustrated: 6) wherein air is cooled by the oxygenenriched product.

A part, about 90 to 97 percent, of the air fed to the nitrogen regenerator 4 is withdrawn, at about 90 to 92 K through conduit 8, and another portion is withdrawn, at about 130 to 230 K., through conduit 9, from the central section of this regenerator. The warmer air from conduit 9 is freed from its residual CO content in adsorber 10 and passed, via conduit 11, where it is mixed with the colder part in conduit 8, and the resultant mixture is fed to the expansion turbine 12. The expanded air at a pressure of about 0.8 to 1.2 atmospheres absolute is introduced into the singlecolumn rectification unit'l4 at the lower end thereof,

via conduit 13.

The air fed to the oxygen regenerator 6 passes through conduit 16 to the condenser-evaporator 17 and, from there, in substantially liquefied form, through conduit 18 and throttle valve 19 into the head of the rectification column 14.

From the sump of the column 14, liquid enriched in oxygen to an extent of 45-55 percent, preferably 47 percent, is conducted through conduit 20 and regulating valve 21 through condenser-evaporator 17, is vaporized, and fed via conduit 22 to one of the oxygen regenerators (illustrated: 7) for warming to normal temperature. It is then withdrawn as product through conduit 23. (In this connection, the oxygen from conduit 23 also with a subatmospheric pressure can, of course, be compressed to the pressure necessary for the further operation.)

The fraction exiting from the head of the rectifying column, enriched in nitrogen and containing about 7.5 percent passes via conduit 24 to the nitrogen regenerator(illustrated: and from there through conduit 25 to the outside.

Referring now to FIG. 2, the air introduced through line 1 is, in this embodiment, first compressed in a blower 2' to an intermediate pressure of L3 atmospheres absolute. The resultant compressed stream is branched; one part, about 66 to 70 percent, passes through conduit 3' to the compressor 2"; and the other part passes to the oxygen regenerator 6 or 7 (illustrated: 6). In the compressor 2" the air is compressed to 2 atmospheres gauge, and is then passed through conduit 3 to one of the nitrogen regenerators 4 and 5 (illustrated: 4).

Withdrawn at the cold end of the regenerator through conduit 8 is the major part of the high pressure ainThe minor part of the high pressure air is only partially cooled and is withdrawn from the central section of the regenerator through conduit 9, where it is then passed to adsorber and is freed from its carbon dioxide'content. The conduit 11 then unites with conduit 8 and leads to theexpansion turbine 12, where the air is lowered in pressure to about 1.1 atmospheres absolute. From there, inturn, conduit 13 leads into the lower section of the rectifying column 14.

1 Conduit 15 is branched off conduit 8, this conduit 15 1 leading to the condenser-evaporator 17. The portion of the air liquefied therein passes as scrubbing liquid via expansion valve 19 in conduit 18 into the head of the rectifying column 14. From the sump of the rectifying column 14, as in FIG. 1, the fraction enriched in oxygen to an extent of 45-55 percent, preferably 47 percent, is withdrawn in the liquid phase and fed, via the regulating valve 21, to the condenser-evaporator 17 where it is vaporized. The vaporized product then passes through conduit 22, one of the oxygen regenerators 6 or 7 (illustrated: 7), and then through conduit 23 to the consumer. As in FIG. 1, the nitrogen-enriched fraction, which still contains about 7.5% 0 passes from. the head of the rectifying column through conduit 24 to one of the nitrogen regenerators 4 or 5 (illustrated: 5), and through conduit 25 to the outside.

ln contradistinction to FIG. 1, the amount of air conducted through one of the oxygen regenerators 6 and 7 (illustrated: 6-) is directly introduced through conduit 30 to the foot of the rectifying column 14 at only slightly superatmospheric pressure.

By the use of an analogous system, it is also possible to employ, in place of the rectifying column 14, a parallel-flow evaporator according to German Pat. No. 589,916, there being suitably provided a vacuum pump for withdrawing the oxygen under suction from the evaporator coil.

From the foregoing description, one skilled in the art caneasily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed is:

1. A process for separating air in a fractionating column to produce an oxygen rich separation product, said process comprising the steps of:

a. compressing the air-to-be-separated to a pressure of l to 2 atmospheres gauge;

b. dividing resultant compressed air-to-be-separated into two branches, cooling all of one branch of said air-to-be-separated to almost liquefaction temperature by heat exchange with a separation product, and cooling substantially all of the other branch of the air-to-be-separated to almost liquefaction temperature by heat exchange with another separation product;

0. liquefying the one branch of the air as liquid air by heat exchange with liquid bottom product withdrawn from the fractionating column in a vaporizer condenser disposed externally of said fractionating column, thereby vaporizing the bottom product and passing all of the vapor thus produced in heat exchange with said one branch of the air-to-be-separated; 4

d. directly throttling the thus liquefied air as sole reflux into the top of the fractionating column; heating the other branch of the air, engine expanding the heated air and passing resultant engine expanded air in the gas phase into the foot of the separation column;

f. fractionating said branches of air-to-be-separated in said fractionating column at a pressure of about 0.8-1 .2 atmospheres absolute.

2. A process as defined in claim 1 wherein-only a fraction of said other part of the portion of the air which is at a pressure of 1-2 atmospheres gauge and whichis to be engine expanded in step (e) is cooled to almost the liquefaction temperature instep (b).

3. A process for separating air in a fractionating column to produce an oxygen rich separation product, said process comprising the steps of:

a. compressingat least a portion of the air-to-beseparated to a pressure of l to 2 atmospheres gauge, the remaining portion being at a pressure below 1 atmosphere gauge:

b. cooling both portions of said air from step (a) to almost liquefaction temperature by heat exchange with a separation product;

cl liquefying as liquid air part of the portion of the air which is at a pressure of 1 to 2 atmospheres gauge and at almost liquefaction temperature, by heat exchange with liquid bottom product withdrawn from the fractionating column in a vaporizer condenser disposed externally of said fractionating column, thereby vaporizing the bottom product and passing all of the vapor thus produced in heat exchange with the portion of air-to-be-separated at a pressure below 1 atmosphere;

d. directly throttling the thus liquefied air as sole reflux into the top of the fractionating column;

e. heating the other, part of the portion of the air which is at a pressure of 1 to 2 atmospheres gauge and cooled to almost liquefaction temperature, en-

gine expanding resultant heated air and passing resultant engine expanded air in the gas phase into the foot of the separation column; f. passing the remaining portion of air from step (b) not treated in steps (0), (d), and (e), in gaseous form into the foot of the separation column; and g. fractionating both portions of said air-tobeseparated in said fractionating column at a pressure of about 0.8-1.2 atmospheres absolute. 4. A process as defined in claim 1 wherein in step (b) a part of said other branch of the compressed air to to be separated is desorbed of CO at a higher temperature; and wherein said heating of said substantially all of said other branch of resultant cooled compressed air is conducted by admixing resultant desorbed part thereto. 7

5. A process in accordance with claim 4, wherein said higher temperature is l30-230 K.

6. A process as defined by claim 4 wherein step (a) is conducted in two stages, said air to be separated being compressed to an intermediate pressure before compression to about 1 to 2 atmospheres gauge, a minor part of said air compressed to an intermediate pressure being cooled and directly passed to the other flow path of said rectification column without being engine expanded, the remaining part of said air compressed to an intermediate pressure being compressed to about 1 to 2 atmospheres gauge for further treating.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 699 695 Dated I QCtOber 24 1972 lnventol-(s) Rudolph Becker It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

COLUMN 6, AFTER CLAIM 6: The following claim is v to be included:

- 7. A process as defined in Claim 3 wherein a fraction of the air-to-be-separated at a pressure of l to 2 atmospheres gauge is desorbed of CO at a temperature substantially higher than the liquefaction temperature thereof, and is employed in step (e) for said heating of the other part of the portion of the air which is at a temperature of l to 2 atmospheres gauge and cooled to almost liquefaction temperature.

the cover sheet [57] "6 claims" should read 7 claims Signed and sealed this 18th day of June 1974 (SEAL) Attest:

EDWARD'MELETCHERJR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM Dc 0376 U.5l GOVERNMENT PRINTING OFFICE 2 I969 O366-334, 

2. A process as defined in claim 1 wherein only a fraction of said other part of the portion of the air which is at a pressure of 1-2 atmospheres gauge and which is to be engine expanded in step (e) is cooled to almost the liquefaction temperature in step (b).
 3. A process for separating air in a fractionating column to produce an oxygen rich separation product, said process comprising the steps of: a. compressing at least a portion of the air-to-be-separated to a pressure of 1 to 2 atmospheres gauge, the remaining portion being at a pressure below 1 atmosphere gauge: b. cooling both portions of said air from step (a) to almost liquefaction temperature by heat exchange with a separation product; c. liquefying as liquid air part of the portion of the air which iS at a pressure of 1 to 2 atmospheres gauge and at almost liquefaction temperature, by heat exchange with liquid bottom product withdrawn from the fractionating column in a vaporizer condenser disposed externally of said fractionating column, thereby vaporizing the bottom product and passing all of the vapor thus produced in heat exchange with the portion of air-to-be-separated at a pressure below 1 atmosphere; d. directly throttling the thus liquefied air as sole reflux into the top of the fractionating column; e. heating the other part of the portion of the air which is at a pressure of 1 to 2 atmospheres gauge and cooled to almost liquefaction temperature, engine expanding resultant heated air and passing resultant engine expanded air in the gas phase into the foot of the separation column; f. passing the remaining portion of air from step (b) not treated in steps (c), (d), and (e), in gaseous form into the foot of the separation column; and g. fractionating both portions of said air-to-be-separated in said fractionating column at a pressure of about 0.8-1.2 atmospheres absolute.
 4. A process as defined in claim 1 wherein in step (b) a part of said other branch of the compressed air to to be separated is desorbed of CO2 at a higher temperature; and wherein said heating of said substantially all of said other branch of resultant cooled compressed air is conducted by admixing resultant desorbed part thereto.
 5. A process in accordance with claim 4, wherein said higher temperature is 130*-230* K.
 6. A process as defined by claim 4 wherein step (a) is conducted in two stages, said air to be separated being compressed to an intermediate pressure before compression to about 1 to 2 atmospheres gauge, a minor part of said air compressed to an intermediate pressure being cooled and directly passed to the other flow path of said rectification column without being engine expanded, the remaining part of said air compressed to an intermediate pressure being compressed to about 1 to 2 atmospheres gauge for further treating. 